In the technique of the injection moulding of plastic material it is known to inject the plastic material in the molten state into a mould through a plurality of nozzles or injection units, generally associated with a distribution plate, also called “hot distribution plate”, usually integrated in the same mould, that has the function of receiving the molten plastic material and of distributing it into the various injection nozzles, so that it is injected into the mould.
It is also known to control the injection of plastic material, in each injection unit, by contemporarily driving a plurality of closing rods or pins, each associated with a respective injection unit, so that each closing rod moves alternately, along its axis, between an open position, in which the tip of the rod sets free an injection hole of the injection unit, whereby the molten plastic material can freely flow into the cavity of the mould, and a closed position, in which the tip of the rod closes the injection hole, so as to interrupt the flow of the fluid plastic material from the injection unit toward the cavity of the mould.
Often, in the jargon of the field of injection moulding, this control system of the multi-rod type, i.e. capable of simultaneously controlling and driving a plurality of closing rods, is also called “table drive”, or “table system”, or with equivalent expressions, since the reciprocating motion of the closing rods is achieved through a plate, that recalls the form of a table, to which each closing rod is connected at one respective end, whereby this plate, while moving alternately between two opposite end positions, contemporarily control and drive all the closing rods to move between their open and closed positions.
In the application and in the use of these driving groups or systems of the multi-rod type, it can happen that an injection unit or nozzle breaks down or is subject in general to a drawback or failure, for instance because the resistance that holds in temperature the same injection unit blows out, or for other causes.
In these circumstances, it is often necessary to intervene in order to repair the broken injection unit, so as to ensure correct operation of the moulding system.
Insofar in the practice it is necessary to disassemble the driving plate of the closing rods, as well as other parts of the system, so as to be able to reach and to intervene in the zone of the broken injection nozzle, i.e. to get off and repair it, and if it is the case to replace it.
Then, in the actual state of the art, a breakdown as that above summarily described, or a similar drawback, involves, in fact, the interruption of the operation of moulding for a period of time that is not negligible, in order to allow to complete the intervention and to make the reparation.
This of course entails a notable loss of time, with a considerable increase in the costs and certainly a negative effect on the overall performance and the efficiency of the moulding operation.